In some communication systems, such as Time Division Multiple Access (TDMA) systems, wireless communication devices operating in these systems are required to monitor multiple channels for radio frequency (RF) activity. For example, a wireless communication device may monitor channels having different priority levels, wherein the device remains on a lower priority channel a majority of the time and periodically leaves the lower priority channel to inspect a higher priority channel for a RF signal of interest. The time that it takes to inspect the higher priority channel and return to the lower priority channel (if no RF signal of interest is present) causes a hole or gap in audio being received on the lower priority channel. The length of that audio hole affects the quality of the audio signal heard by a user of the wireless communication device. Thus, it is desirable to shorten the duration of the channel inspection on the higher priority channel to a minimum amount of time in order to maximize the audio quality of an RF signal on the lower priority channel.
One method used for minimizing the duration of an audio hole is called channel marking, which uses the results from one channel inspection to make assumptions about what to expect during the next channel inspection of the same channel. During the channel marking process, if a channel is not marked, a full inspection is performed to validate whether or not RF activity on the channel is of interest. If the activity is not of interest, the channel is “marked” to cause the communication device to perform only a partial channel inspection upon next returning to the channel. The partial inspection is of a shorter duration, which thereby shortens the duration of the audio hole associated with the partial inspection.
In accordance with one known channel marking technique, during the partial channel inspection, if the communication device finds any RF activity on the channel at all, the communication device assumes that it is the same activity that was present during the full channel inspection. This assumption is valid and the method effective if an idle gap of no RF activity exists between media transmissions on an RF channel that can be used to clear the channel mark, and if only one type of call occurs on the channel. However, this assumption may not be valid in some system implementations, such as in 2-slot TDMA systems, for a number of reasons.
For instance, where multiple media paths (e.g., slots in a TDMA system) exist for a single radio frequency, channels are likely not idle between separate media transmissions because even if one slot is idle, the other slot may be busy, thereby causing the repeater to transmit a signal on that frequency. Thus, a method based on RF energy alone could not differentiate one signal on a slot from a different signal on another slot of the same radio frequency. In addition, where voice, data and control signals appear on the same slot, with data signals filling idle gaps between voice transmissions, wide assumptions based on RF energy alone are ineffective in verifying that the same signal exists on the slot during a subsequent inspection.
Thus, there exists a need for a method for channel inspection that addresses at least some of the above-mentioned shortcomings.
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